We don't exactly know how the outcome of the trials has affected Sam's mental and physical health, but it's important to think about it in terms of kick-starting season 9.
Obviously, there won't be a magical cure to make him feel better, and if so, it would certainly take all the drama away from the story. Unlike his hallucinations in season 7, which were cured with Castiel's help, no one has the ability to help him now. The damage is quite extensive and the most likely choice is to find a cure or to find God, which would take another season. Right now, it doesn't look very good for the Boy King.
The pastSeason 8 has given Sam a human story, exposing his desires to have a normal life, which collided with Dean's desires to have his brother by his side. Amelia's story is not exactly the best way to do that, and the fact that the show let her disappear into the never-be-mentioned-nirvana is quite telling. Both Benny and Amelia were plot-devices used to highlight the conflict between the brothers in the first half of season 8. The problems were contrived, given the fact that Sam didn't look for Dean in the first place. It's a choice that I consider widely out of character for him, but there is nothing fans can do about it now. On top of that, his resentment of Benny didn't really feel organic at all. Sam used to be someone who could see the good in people, be it monsters or not. If the show brings Benny back, I would like to see Sam and Benny interacting on a level that shows more acceptance between them. Benny is very popular and alienating Sam from popular characters never really works.
Men of LettersI've been waiting for a story that connects Sam's wish to be normal with the supernatural aspect. The show managed to give Sam exactly that. It gave him a home and a destiny to fulfill; something that makes him feel worthy.
It is a legacy passed on by Henry Winchester, which connects both brothers to the mythology, although Sam's affinity for researching gives him a bit of an edge. The MoL were researchers and not hunters, after all. It's no wonder Sam thrives in an academic environment and it's refreshing to see him enjoying things once in a while. He has a home and it gives him a feeling of normalcy. Bonus: He has Dean by his side.
Sam grew up in an environment where his independence was compromised in favor of doing the family business. He's a character who actively searches for his place in the world, and he doesn't shy away from wanting something for himself. It's much healthier than Dean's attitude, but it still causes problems when the show refuses to give him more friends to interact with.
He's close to Jody Mills and is on friendly terms with Kevin, Charlie, Castiel and Garth, but not many people put him first. We don't see how his mind works, what his desires and hopes for the future are. Saying he wants normal is not the same as discovering why he wants it in the first place. We didn't even see his room in the bunker, which is a stark contrast to Dean's emotional exposure.
It's difficult to relate to Sam when we don't even know what makes him tick.
And that is something that will hopefully be addressed in season 9. The previous season continued isolating him from other people, while Dean got to interact with others. Sam's character flaws are only highlighted with contrived conflicts, and it doesn't help that people get the impression that "he's selfish", "he is jealous", "he doesn't put Dean first". Isolating him from Dean and other people just brings out the worst in him, and I don't see the point in showing how he didn't even bother to look for Dean. Sam Winchester is much better than that. He actively wants to be a better person. He also wants to be "pure" and not tainted by demon blood or other external flaws, which brings us to another issue.
StrengthPeople always say how Dean is the one with an extreme lack of self-worth, but I would argue that he's not the only one. Sam sees himself as a monster, a constant failure to the most important person in his life. Giving him one illness after another (demon blood, no soul, hallucinations, trials) doesn't help in that regard. It's like kicking a person who's already down.
I see no point in a storyline that constantly exposes weaknesses instead of strength, which is why I would have enjoyed seeing Sam trying to save Dean from Purgatory.
It would certainly be interesting to see how Sam overcomes his illness and manages to help Dean. He can be just as much of a support system as his brother. And it helps him with his issues, including his constant belief that he's nothing but a disappointment to others. A success gives him the confidence he needs and the emotional exposure he deserves.